The Elemental Estimate layout and grouping of items will be used in this example. When building up composite rates for Approximate Quantities, you have to follow some basic principles. We are going to illustrate a composite rate build-up for the Roof:

First, you have to determine the Group unit of measurement. When you are measuring the Roof in Elemental or Approximate Quantities estimating, the group unit of measurement is the square metre (m2) on flat area or sloping surface. We will use the flat area.

Step 2

The second step is listing all associated Bill items that can be mapped to the Roof by area. These are:

The next step is listing all associated Bill items that can be linked to the Roof. These are items which cannot be mapped to the area.

Timber Roof Construction:

Timber roof construction has members which are measured in metres and number. In order to convert the members of roof construction to cost per square metre, we should associate them to the flat area between two trusses. The trusses are spaced at 1200mm centres, and the base length of the truss is 7020mm. The flat area between trusses is 7.020 x 1.200m

Rate Build Up for mappable items (areas). Since your Group unit is the square metre (m2), you should convert the Bill item rates to Cost per Square Metre:

Rate Build Up

GROUP – ROOF

Rate – Cost Per Square Metre (m2) Rands

1m2 IBR Roof Covering

1m2 = R155

155

1m2 Super Sisalation Insulation

1m2 = R25

25

1m2 Plasterboard Ceiling

1m2 = R35

35

1m2 Paint to Ceilings

1m2 = R40

40

1m2 Paint on IBR Roof Covering

1m2= R40

40

Composite Rate – ROOF

295

The composite rate for items which can be mapped to the Flat Roof Area is R295 per square metre.

Step 5

Rate Build Up for Timber Roof Construction:

Timber roof construction requires a Rate Build Up for items which cannot be mapped to Roof Area. The flat area between trusses is 7.020 x 1.200m.To convert the Bill item rates to Cost per Square Metre, we have to use principles that are used in building up composite rates for Windows. In this case, the flat area between trusses (7.020×1.200)m should be treated as a single entity (Think of a single window). This allows us to link associated items to this single entity, for example, we can link items in Step 3 to this entity. We will then find the total cost of items in this entity, and then convert the cost to cost per square metre:

Rate Build Up

GROUP – ROOF CONSTRUCTION

Rate – Cost Per Flat Area (7020×1200) Rands

1No. Truss (7020x1100mm)

1No = R900

900

Wall Plate

Flat area has 1200mm wall plate each side: 2 x 1200mm = 2400mm

2.4 x R22 = R52.80

52.80

Angle Brackets to Truss and Wall Plate

1 Truss has 2 fixing brackets each side: 2 x 2 = 4

4 x R2.00 = R8.00

8.00

Purlin Clips

Pair of Hurricane purlin clips on each purlin/rafter connection.

Four purlins on each side of truss: 4 x 2 = 8 purlins.

Number of clips = 8 x 2 = 16 No.

16 x R2.00 = R32.00

32.00

Hoop Iron Tie Built into Brickwork

Wall plate with ties built into brickwork @ 1000mm centres.

Therefore 2 x 1200mm of wall plates have 2 ties each.

2 x 2 = 4 Ties

4 x R2.00 = R8.00

8.00

Diagonal Bracing

Diagonal bracing length = 4.392m

Bracing btwn two trusses = 4.392/2 =2.196m

2.196 x 2 sides = 4.392m

4.392 x R22.00 = R96.62

96.62

Purlins

4 x 2 sides =8 Purlins

8 x 1.200m = 9.6m

9.6 x R19.00 =R182.40

182.40

Longitudinal Binders

5 x 1.200m = 6.00m

6 x R20.00=R120

120

Composite Rate – ROOF CONSTRUCTION

1399.82

The composite rate for ROOF CONSTRUCTION is R1399.82 per Flat Area (7020×1200). Now we have to convert this rate to Cost Per Square Metre:

Step 6

Convert Composite Rate to Cost Per Square Metre

You can convert this rate to Cost Per Square Metre for the Elemental Estimate:

Flat Area between two trusses 7020 x 1200,

Area = 7.020 x 1.200 = 8.424m2

Therefore, cost is R1399.82 per 8.424m2

Elemental Rate = R166.17 per m2

Step 7

Add up the rates to get the Total Rate: 295 + 166.17 = R461.17 per square metre.

Total Composite Rate for Approximate Quantities = R461.17 per m2

Elemental Layout and Grouping

Items which go into the element ROOF and components Construction, Coverings and Insulation are stated in the description: